Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2/00—Processes of polymerisation
  • C08F2/12—Polymerisation in non-solvents
  • C08F2/16—Aqueous medium
  • C08F2/22—Emulsion polymerisation
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F14/00—Homopolymers and copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen
  • C08F14/18—Monomers containing fluorine

Definitions

• the present invention relates to a process for polymerizing or copolymerizing fluorinated monomers in an aqueous dispersion, in the presence of radical starters, characterized in particular by a much higher polymerization rate than the one attainable with the known processes under analogous operative conditions.
• the fluoroolefins exhibit different reactivities in the polymerization process, some of them having very low or no reactivities in comparison with tetrafluoroethylene (TFE).
• TFE tetrafluoroethylene
• C3F6 may be cited as an example.
• some perfluorovinylethers exhibit a very low reactivity in polymerization with respect to the other fluoroolefins, in particular with respect to TFE (see US-A-3 132 123).
• FEP thermoplastic copolymer C2F4-C3F6
• a content of 5-25% by weight of C3F6 it is necessary to operate with a high concentration of C3F6 in the gas phase, corresponding to a total pressure of the monomers in the range of from 3.4 to 3.9 MPa abs. (35 to 40 kg/cm2 abs.) (see US-A-3 132 124).
• EP-A- 247 379 discloses a process for polymerizing or copolymerizing fluorinated monomers in an aqueous dispersion by using radical starters and fluorinated surfactants, in the presence of a perfluoropolyether having neutral end groups which is liquid under the poolymerization conditions and is in the form of an aqueous emulsion.
• This process exhibits a very large number of advantages in comparison with the usual polymerization in the absence of perfluoropolyether, while it raises some problems as regards the reproducability of the emulsion when it is carried out with autoclaves of large volume.
• the process requires the use of considerable amounts of perfluoropolyether in order to obtain significant effects on the polymerization rate, which, as is well-known, leads to a considerable increase in costs.
• the emulsion must be prepared immediately before use and cannot be stored, due to the limited shelf life of the perfluoropolyether emulsions.
• microemulsion is used to designate a system in which the perfluoropolyether having neutral end groups is solubilized by a surfactant solution to provide a monophase solution which is stable for a long time without needing dispersion energy.
• the microemulsion may be prepared by simple mixing of the components water, perfluoropolyether having neutral (inert) end groups and a fluorinated surfactant, in particular, of the type of perfluoropolyether having carboxylic end groups or cationic end groups.
• a fluorinated surfactant in particular, of the type of perfluoropolyether having carboxylic end groups or cationic end groups.
• Microemulsions form by simply mixing the components at a temperature at which the microemulsion is stable without having to supply a considerable dispersion energy as in the case of conventional emulsions where the use of high dispersion energies (e.g. provided by Ultraturrax®, ultrasound and fast dispersion means) is always required.
• high dispersion energies e.g. provided by Ultraturrax®, ultrasound and fast dispersion means
• microemulsions are thermo-dynamically stable systems within a certain temperature range, i.e., they tend to undergo phase separation outside said temperature range but form again spontaneously by simple mixing once they are inside said temperature range.
• microemulsion preparation is reproducible, is not influenced by volume effects and provides a system in which the interphase area is very large. This allows to transfer polymerization recipes from a laboratory scale to a commercial scale without problems, and to sensibly reduce - the polymerization kinetics being the same - the perfluoropolyether amount which is present in the polymerization medium.
• the perfluoropolyether is in the form of a microemulsion at the moment of its addition to the polymerization medium while it does not necessarily have to be in this form once it is diluted with the solution in the autoclave.
• Any perfluoropolyether composed of sequences of perfluorooxyalkylene units can advantageously be utilized.
• the mean molecular weights of the perfluoropolyethers can vary over a wide range starting from a value of about 500.
• perfluoropolyethers with a molecular weight ranging from 600 to 3000.
• Suitable perfluoropolyethers are, for example, the ones of the following classes: with a random distribution of the perfluoro-oxyalkylene units, where R f and R′ f , the same or different from each other, are -CF3, -C2F5 or -C3F7; 2) R f O(CF2CF2O) n (CF2O) m R′ f with a random distribution of the perfluoro-oxyalkylene units, where R f and R′ f , the same or different from each other, are -CF3 or -C2F5; with a random distribution of the perfluoro-oxyalkylene units, where R f and R′ f , the same or different from each other, are -CF3, -C2F5 or -C3F7; where R f and R′ f , the same or different from each other, are -C2F5 or -C3F7; 5) R f O(CF2CF2
• Perfluoropolyethers of class 1) are commercially known under the trademark Fomblin ® Y or Galden ® ; the ones of class 2), under the trademark Fomblin ® Z, all of them being manufactured by Montedison.
• the amount of perfluoropolyether to be used in the process of the invention is very low.
• the amount is of the order of 0.05-2 ml per liter of aqueous polymerization solution.
• the preferred amounts are 0.4 - 1.5 ml per liter.
• radical starter it is possible to use any type which is well known for the polymerization of fluorinated monomers in aqueous dispersion.
• Peroxidized compounds in general are suitable; among the former, potassium or ammonium persulphates are particularly suitable.
• organic peroxides there are suitable both those which are water-soluble, such as disuccinyl peroxide, and those which are water-insoluble (see for example EP-A-75,312).
• radical starters of the azo-type such as, e.g., the ones described in US-A-2 515 628 and 2 520 338. When it is desirable to operate at low polymerization temperatures (for example from 10 to 50°C), a redox starter can be used.
• the radical starter amount is the one which is usually employed in the polymerization of fluoro-olefins: it ranges from 0.003 to 2% by weight referred to the total amount of polymerized monomers.
• the radical starter or -depending on the specific case- the redox system components can be introduced into the reactor at the beginning of the polymerization, or can be gradually added in the course of polymerization.
• the surfactant required to stabilize the latex particles is contained in part or in whole in the neutral perfluoropolyether microemulsion. Generally, the surfactant contained in the microemulsion is sufficient for the polymerization process.
• Suitable surfactants are the known ones, which consist of perfluorinated compounds, in particular those having: 6 to 11 carbon atoms, of the class of carboxylic and sulphonic acids.
• surfactants are those of the class of the perfluoropolyethers having one or two acid end groups.
• the perfluoropolyether microemulsion must be introduced into the aqueous at the beginning of the polymerization: no assumption is made with respect to the perfluoropolyether dispersion degree after the microemulsion has been diluted in the polymerization medium: it could be still in the form of a microemulsion, or in a less finely particled state. Probably, however, the perfluoropolyether dispersion degree is significantly higher than the one attainable by the process according to EP-A- 247 379. Subsequently, the other ingredients (monomers, starters, molecular weight regulators, if any) are introduced.
• thermoplastic copolymer ClFC CF2/ethylene (type Halar®).
• the process according to the invention offers, besides the advantages described hereinbefore, also the same advantages (possibility to operate at lower polymerization pressures than the ones of the prior art) which are illustrated in EP-A- 247 379 relating to the copolymerization of fluorinated monomers.
• a particular feature of the process of the present invention is the obtainment of aqueous fluoropolymer dispersions characterized by an extremely high number of particles per liter and by an extremely small diameter of the particles. Typical examples of numbers of polymer particles per liter are of the order of 0.5 - 5.1018.
• a further characteristic of the process of the present invention is that -with the same polymerization kinetics- the utilized perfluoropolyether amount is lower by about one order of magnitude than the one indicated in the examples of EP-A- 247 379 and this leads to the above mentioned advantages.
• the resulting dispersion was heated to 75°C under slight stirring. A perfectly limpid solution was obtained. Upon cooling to room temperature, the solution separated into two phases, but the system proved to be reversible on heating. The system was identified as a microemulsion stable in the range of 60 - 90°C. 15.3 ml of the microemulsion at 75°C, which obtained 2 ml of the above neutral perfluoropolyether, were added to 2 l of carefully deaerated water in a 4.2 l autoclave made of steel AISI 316, equipped with a mechanical stirrer, in which vacuum had previously been generated.
• the temperature in the autoclave was brought to 95°C under mechanical stirring (600 rpm).
• the pressure was brought to 1.9 MPa (20 kg/cm2) gange, using a gaseous mixture containing 63% By moles of C3F6 and 37% of C2F4.
• 62 ml of an aqueous solution prepared by dissolving 0.73 g of (NH4)2S2O8 and 0.73 g of K2S2O8 in 500 ml of H2O were then introduced into the autoclave.
• a C3F6/C2F4 mixture containing 5.8% by moles of hexafluoropropene.
• the mean diameter of the dispersion particles was 0.041 ⁇ m.
• the number of particles per liter of water (N p/1 ) was equal to 2.9.1018.
• the aqueous dispersion was coagulated by mechanical stirring, was filtered and the solid product was repeatedly washed with distilled water and dried in a fan cooled oven at 200°C.
• the product had a M.F.I. (melt flow index) of 0.65 g/10 minutes and a second melt peak at 262.4°C.
• the resulting powder was extruded in a Brabender single-screw extruder. Regular and perfectly white pellets were obtained. The product did not need any further stabilization and whitening treatment.
• the thermovolatility index was 59 and the whiteness was 71.
• the reaction was stopped after 65 minutes and the latex was discharged.
• An aqueous dispersion containing 225 g/l of a polymeric resin was obtained.
• the average diameter of the particles was determined by electron microscopy and was 0.046 ⁇ m, corresponding to a number of particles per litre of water of 2.2 . 1018.
• the coagulated powder exhibited a melt flow index of 0.92 and a specific absorbance ratio of 3.5.
• the suspension was stirred for 5 minutes by means of an Ultraturrax ® stirrer mod. T65 (10,000 rpm) manufactured by IKA Werke. There was added an aqueous solution containing 4 g of having an equivalent acidimetric molecular weight of 690. The emulsion so obtained was homogenized for a further 5 minutes. The dispersion was fed into a steel AISI 316 autoclave of 4.2 liter volume, wherein vacuum had previously been generated. Distilled water was added up to a total volume of 2,000 ml.
• the temperature in the autoclave was brought to 95°C; the pressure was brought to 1.9 MPa (20 kg/cm2) gauge using a gaseous mixture containing 62% by moles of C3F6 and 38% by moles of C2F4.
• 62 ml of an aqueous solution obtained by dissolving 0.73 g of (NH4)2S2O8 and 0.73 g of H2S2O8 in 500 ml of H2O were then introduced into the autoclave.
• the pressure in the autoclave began to decrease, it was brought to the initial value by feeding, through a compressor, a C3F6/C2F4 mixture containing 6.7% by moles of hexafluoropropene.
• the above-mentioned persulphate solution was fed at a rate of 88 ml/h. Stirring in the reactor was conducted for 65 minutes, whereafter it was stopped and the reactor content was discharged.
• the aqueous dispersion was coagulated by mechanical stirring and was filtered; the solid product was repeatedly washed with distilled water and was dried in a circulating air oven at 200°C.
• the product had a specific melt viscosity of 1.063 x 108 mPa ⁇ s (1.063 x 10 poise) and a melt flow index (M.F.I.) of 0.5 g/10 minutes and exhibited a second melting peak at 264.9°C.
• the resulting powder was extruded in a Branbender single-screw extruder: regular and perfectly white pelletes were obtained.
• the product did not require any further stabilizing and whitening treatment.
• the thermovolatility index was 60 and the whiteness was 71.
• microemulsion so prepared was added, at a temperature of 75°C, to 3 l of thoroughly deaerated water, contained in an AISI 316 steel autoclave of 4.2 l volume, equipped with a mechanical stirrer, in which vacuum had previously been generated.
• the temperature in the autoclave was brought to 95°C under mechanical stirring (600 rpm).
• the autoclave was pressurized to 1.9 MPa (20 kg/cm2) gauge with a gas mixture containing 11.57% by moles of perfluoromethylvinylether C3F6O and 88.43% of C2F4.
• the average C3F6O content in the polymer was 3.1% by moles.
• the autoclave was brought to 30°C, whereafter 100 mg of (NH4)2S2O8 were introduced and the pressure was brought to 1.9 MPa (20 atm.) by means of a mixture of TFE and perfluoromethylvinylether (PFMVE) (1.6% by moles of PFMVE comonomer).
• PFMVE perfluoromethylvinylether
• N p/1 The number of particles per liter of water (N p/1 ) was equal to 5.2 x 1017.
• the comonomer content (PFMVE) of the coagulated polymer was 0.62% by weight.

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• Polymerisation Methods In General (AREA)

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• 1986
  • 1986-06-26 IT IT20909/86A patent/IT1204903B/it active
• 1987
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